1. Field of the Invention
The present invention relates to an electro-optical device typified by an EL (electroluminescence) display device formed by fabricating semiconductor elements (elements using a semiconductor thin film) on a surface of a substrate, and an electronic device including the electro-optical device as a display. Particularly, the invention relates to a method of manufacturing the same.
2. Description of the Related Art
In recent years, a technique for forming a thin film transistor (hereinafter referred to as a “TFT”) on a substrate has made remarkable progress, and its application and development to an active matrix type display device has proceeded. Especially, since a TFT using a semiconductor film that has a crystal structure (e.g., a polysilicon film) has a field effect mobility higher than a conventional TFT using an amorphous silicon film, a high speed operation can be made. Thus, it becomes possible to form a driving circuit that is connected to a pixel portion from the TFT, and to form the driving circuit on the same substrate.
Attention has been paid to such an active matrix type display device since various merits, such as reduction of manufacturing cost, miniaturization and thinning of a display device, increase of yield, and increase of throughput, can be obtained by forming various circuits and elements on the same substrate.
In the active matrix type EL display device, a switching element made of a TFT is provided for each pixel, and a driving element for making current control is operated by the switching element, so that an EL layer (light emitting layer) is made to emit light. For example, there is an EL display device disclosed in U.S. Pat. No. 5,684,365 (see Japanese Patent Application Laid-open No. Hei 8-234683), or Japanese Patent Application Laid-open Publication No. Hei 10-189252.
In methods of color display by these EL display devices, there have been trials of arranging EL layers which emit light of the three primary colors red (R), green (G), and blue (B) in each pixel. However, nearly all of the materials generally used as EL layers are organic materials, and it is difficult to apply a photolithography technique used in micro-machining as is. The reason is that the EL materials themselves are extremely weak with respect to moisture, and their handling is difficult in that they will easily dissolve in even a developer solution.
A technique of forming the EL layers by an ink-jet method has been proposed as a technique of solving these types of problems. For example, in Japanese Patent Application Laid-open No. Hei 10-012377 an active matrix type EL display in which the EL layer is formed by the ink-jet method is disclosed. Further, a similar technique is also disclosed in Shimada, T., et al., “Multicolor Pixel Patterning of Light-Emitting Polymers by Ink-jet Printing,” SID 99 DIGEST, pp. 376-379.
It becomes possible to form an EL layer for each single pixel with the ink-jet method, and a process of patterning after forming the EL layer can be omitted. However, for both an active matrix type EL display device and for a passive type EL display device, as the screen size becomes larger and the pixel density increases, requirements for high positional precision and high speed processing increase.